The invention relates to an indicating instrument which can be inserted by means of a housing having an external thread into a recess in a dashboard and can be fixed on the dashboard, in particular of a vehicle, by means of a housing nut which can be screwed onto the external thread and has an internal thread.
Indicating instruments of the abovementioned type are mainly installed retrospectively into existing dashboards, for example in watercraft, and are generally known. Their housing either has a collar, by means of which it bears from the rear side against the edge of a recess of the dashboard, or else it is provided with a plurality of latches which are able to snap behind this dashboard when the housing is pushed into the recess of the dashboard. The housing nut is then screwed from the front side onto the housing, so that the housing is clamped firmly to the dashboard between the latches and the housing nut. The thread is a flat thread having a small pitch, which is necessary in order to impart the clamping forces via a number of thread turns of the nut and in order to obtain self-locking.
Since such indicating instruments are installed in dashboards which differ in thickness, and in order to compensate for tolerances, in the case of thin-walled dashboards the housing, after being pushed into the dashboard, has to considerably protrude forward out of the dashboard. This leads to many revolutions of the housing nut being necessary in order to tighten the latter, which is costly in terms of time and is perceived as a nuisance.
The invention is based on the problem of designing an indicating instrument of the type mentioned at the beginning in such a manner that its housing nut can be brought as rapidly as possible into its clamping position on the housing.
According to the invention, this problem is solved in that either the external thread and the internal thread are only provided in at least two subregions of the circumference of the housing and of the housing nut, respectively, subregions without a thread being in each case arranged in the circumferential direction between the subregions having a thread, so that the housing nut can be pushed in at least two angular positions completely onto the housing without engagement in the external thread, or in that only the external thread or the internal thread is provided in at least two subregions of the circumference and these subregions are of resilient design radially in a position in which the internal thread and external thread become disengaged.
This design makes it possible for the housing nut to be able to be pushed axially onto the housing initially without turning it until it is directly in front of the dashboard. Only when it slightly touches the dashboard are the internal thread and external thread brought into permanent engagement, by rotation of the threaded nut, a rotation of a few angular degrees sufficing to produce the required clamping force. If the resilient subregions are provided, these are initially able xe2x80x9cto gratexe2x80x9d over the other thread as the housing nut is being pushed on. The invention therefore renders the prolonged rotation of the threaded nut superfluous and enables very rapid installation of indicating instruments of this type.
In spite of the extremely short installation time which is possible, the housing nut is able to impart high clamping forces if, according to a development of the invention, the external thread and the internal thread are designed as self-locking flat threads.
An especially rapid installation of the indicating instrument is possible if the housing has latches which, after insertion of the housing into the recess, grip behind the dashboard from the rear side, and in this latched position the external thread protrudes forward out of the recess, and if the housing nut is designed for fastening on this external thread which protrudes forward.
The housing nut can be pushed axially in three different angular positions onto the housing without the thread being in the way here if the external thread and the internal thread are provided in three subregions of the circumference. Sufficiently high forces can be imparted by means of the three threaded regions. Furthermore, a symmetrical application of force is produced.
The radial springing away of the thread as the housing nut is being pushed on axially can be implemented in a particularly simple manner if, according to another advantageous development of the invention, the internal thread is provided on spring tongues which each form a subregion of the outer surface of the housing nut. By means of this embodiment, a particularly slight xe2x80x9cgratingxe2x80x9d of the internal thread over the external thread can be achieved.
The threaded nut is able to produce high clamping forces, without making it harder to push it on axially, if the internal thread and the external thread each have a serrated profile and the respectively horizontal flank of the internal thread and external thread is provided on the side from which the housing nut is screwed onto the housing.
In the clamping position, the housing nut is forcibly secured against working loose if, according to another embodiment of the invention, the internal thread is provided with latching lugs which can be latched into those subregions of the external thread which are not provided with a thread.
In an indicating instrument according to the invention, in which the external thread and the internal thread are provided only in at least two subregions of the circumference of the housing and of the housing nut, respectively, the installation is advantageously particularly simple if the subregions having a thread each have a shorter length than the subregions which lie between them and do not have a thread, with the result that when the parts are joined, the housing nut does not have to be positioned exactly opposite the housing.
According to another advantageous development of the invention, the housing can be inserted from the front into the recess and can be placed with a step against the dashboard, the external thread is arranged in a region of the housing on the rear side of the dashboard, and the housing can be clamped against the step by means of the housing nut. In this case, the housing is screwed against the dashboard from behind with the result that a visually displeasing and space-taking housing nut is not arranged on the front side of the dashboard facing someone looking at it.
Good sealing, which is important particularly in the case of watercraft, between the housing and dashboard can advantageously be achieved if an O-ring can be arranged between the step of the housing and the dashboard. By means of the arrangement of the O-ring and compression thereof during tightening of the housing nut, penetration of moisture into the dashboard is prevented in a simple manner.